As far as I remember, there is some truth behind this statement: glass is inherently extremely strong, but it is fragile in practice because of microcracks on its surface. In water, glass dissolves to some extent. As a result, microcracks partly disappear, and glass becomes much stronger (at least for a while). I remember reading that A. F. Ioffe (I guess his name was sometimes written as Joffe) held a thin glass stick in water for a few days, and the stick became flexible. Maybe I'll try to find a reference later.
EDIT: the following article confirms that holding glass in water can make the glass stronger, but the authors used hot water:
Stockdale, G. F., Tooley, F. V. and Ying, C. W. Changes in the Tensile Strength of Glass Caused by Water Immersion Treatment. Journal of the American Ceramic Society, vol. 34, no. 4, p.116, 1951. doi: 10.1111/j.1151-2916.1951.tb11618.x